1. Field of the Invention
The present invention relates generally to composite high-frequency components and, more particularly, to a composite high-frequency component formed by connecting a high-frequency component such as a high-frequency switch component and a filter component.
2. Description of the Related Art
Referring to FIG. 10, a high-frequency switch component is used to selectively establish a connection between a transmitting circuit TX and an antenna ANT and a connection between a receiving circuit RX and the antenna ANT.
Referring to FIG. 11, a high-frequency switch component 1 is connected to an antenna ANT, to a transmitting circuit TX and to a receiving circuit RX. The anode of a diode D1 is connected to the transmitting circuit TX through a capacitor C1. The anode of the diode D1 is also connected to ground potential through a series circuit of a distributed constant line L1 and a capacitor C2. If the wavelength of a transmitted signal from the transmitting circuit TX is .lambda., the line length of the distributed constant line L1 is set to .lambda./4 or less. A control terminal Vc1 is connected to a point of connection between the distributed constant line L1 and the capacitor C2. A control circuit for switching the high-frequency switch component 1 is connected to the control terminal Vc1. The cathode of the diode D1 is connected to the antenna ANT through a capacitor C3. A series circuit of a distributed constant line L2 and a capacitor C4 is connected in parallel with the diode D1 (between the anode and the cathode).
To the capacitor C3 connected to the antenna ANT, the receiving circuit RX is connected through a series circuit of a distributed constant line L3 and a capacitor C5. The line length of the distributed constant line L3 is also set to .lambda./4 or less, as in the case of the distributed constant line L1. The anode of a diode D2 is connected to a point of connection between the distributed constant line L2 and the capacitor C5. The cathode of the diode D2 is connected to ground potential through a capacitor C6. A control terminal Vc2 is connected to a point of connection between the diode D2 and the capacitor C6. The control circuit for switching the high-frequency switch component 1 is connected to the control terminal Vc2 as well as to the terminal Vc1.
To perform transmitting by using the thus-arranged high-frequency switch component 1, a positive bias voltage is applied to the control terminal Vc1 while a negative bias voltage is applied to the control terminal Vc2. These voltages act as forward bias voltages on the diodes D1 and D2 to turn on diodes D1 and D2. At this time, DC components are blocked by the capacitors C1 to C6 and the voltages supplied to the control voltages Vc1 and Vc2 are applied only to the circuits which include the diodes D1 and D2. Accordingly, the distributed constant line L3 is grounded by the diode D2 and resonates at a transmitting frequency, so that the impedance thereof becomes substantially infinitely large. Therefore, substantially no transmitted signal from the transmitting circuit TX is transmitted to the receiving circuit RX. The transmitted signal is transmitted to the antenna ANT via the capacitor C1, the diode D1 and the capacitor C3. Since the distributed constant circuit L1 is grounded through the capacitor C2, it resonates at the transmitting frequency, so that the impedance thereof becomes substantially infinitely large. The transmitted signal is thereby prevented from leaking to ground.
On the other hand, at the time of receiving, a negative bias voltage is applied to the control terminal Vc1 while a positive bias voltage is applied to the control terminal Vc2. These voltages act as reverse bias voltages on the diodes D1 and D2 to turn off diodes D1 and D2, so that a received signal from the antenna ANT is transmitted to the receiving circuit RX via the capacitor C3, the distributed constant line L3 and the capacitor C5, and is not substantially transmitted to the transmitting circuit TX.
As described above, the high-frequency switch component 1 can switch transmitted and received signals by controlling the bias voltages applied to the control terminals Vc1 and Vc2.
The series circuit of the distributed constant line L2 and the capacitor C4 is used to reduce the insertion loss and reflection loss by increasing the impedance at the point of connection between the diode D1 and the distributed constant line L2 when the diode D1 is off by forming a parallel resonant circuit. It resonates by the combined electrostatic capacitance of the diode D1 in the off state and the capacitor C4 and the inductance component of the distributed constant line L2, at the frequency of the received signal.
Conventionally, a composite high-frequency component is made by connecting a filter component to the above-described high-frequency switch component. However, the high-frequency component and the filter component are designed and manufactured separately from each other. Therefore, the area and the volume occupied by these components on a circuit board are large, so that the flexibility of the circuit arrangement is reduced.
It is also necessary to newly add an impedance matching circuit to the high-frequency component and the filter component for the purpose of impedance matching between the high-frequency component and the filter component.
Further, additional design time is required for designing the impedance matching circuit.